Heart sound tracking system and method

ABSTRACT

A system and method provide heart sound tracking, including an input circuit, configured to receive heart sound information, and a heart sound recognition circuit. The heart sound recognition circuit can be coupled to the input circuit and can be configured to recognize, within a particular heart sound of a particular heart sound waveform, a first intra heart sound energy indication and a corresponding first intra heart sound time indication using the heart sound information from the particular heart sound waveform and the heart sound information from at least one other heart sound waveform. The particular heart sound can include at least a portion of one of S1, S2, S3, and S4. Further, the first intra heart sound energy indication and the corresponding first intra heart sound time indication can correspond to the at least a portion of one of S1, S2, S3, and S4, respectively.

TECHNICAL FIELD

This patent document pertains generally to cardiac health, and moreparticularly, but not by way of limitation, to heart sounds tracking.

BACKGROUND

Heart sounds are generally associated with the mechanical vibrationsfrom the activity of a subject's heart and the flow of blood through theheart. Because of this association, heart sounds typically recur witheach cardiac cycle of a heart, and are typically separated andclassified into one of four types according to the activity associatedwith the vibration: S1, S2, S3, and S4. S1 (commonly referred to in theart as “the first heart sound”) is typically associated with thevibrational sound made by the heart during tensing of the mitral valve.S2 (commonly referred to in the art as “the second heart sound”) istypically associated with the beginning of diastole. S3 (commonlyreferred to in the art as “the third heart sound”) and S4 (commonlyreferred to in the art as “the fourth heart sound”) are typicallyassociated with the filling pressures of the left ventricle duringdiastole. Generally, heart sounds can be used as indications of properor improper functioning of a subject's heart.

OVERVIEW

A heart sound is typically identified according to its amplitude andcorresponding timing. In one example, a heart sound can be detectedusing a heart sound window established according to certain triggeringevents, such as certain components of an electrocardiogram (“ECG”)signal. One method of identifying the heart sound includes detecting themaximum heart sound amplitude within the heart sound window. The heartsound, for that heart sound window, is then identified according to thevalue of the maximum heart sound amplitude and corresponding timing ofthe maximum amplitude. However, multiple peaks can be present within theheart sound signal of an individual heart sound. The present inventorshave recognized, among other things, that the peak in the heart soundsignal having the maximum amplitude may not be a desirable identifier ofthe heart sound.

This document discusses, among other things, a system and method forheart sound tracking, including an input circuit, configured to receiveheart sound information, and a heart sound recognition circuit. Theheart sound recognition circuit can be coupled to the input circuit andcan be configured to recognize, within a particular heart sound of aparticular heart sound waveform, a first intra heart sound energyindication and a corresponding first intra heart sound time indicationusing the heart sound information from the particular heart soundwaveform and the heart sound information from at least one other heartsound waveform. The particular heart sound can include at least aportion of one of S1, S2, S3, and S4. Further, the first intra heartsound energy indication and the corresponding first intra heart soundtime indication can correspond to the at least a portion of one of S1,S2, S3, and S4, respectively.

In Example 1, a system includes an input circuit, configured to receiveheart sound information. The system also includes a heart soundrecognition circuit, coupled to the input circuit, configured torecognize, within a particular heart sound of a particular heart soundwaveform, a first intra heart sound energy indication and acorresponding first intra heart sound time indication using the heartsound information from the particular heart sound waveform and the heartsound information from at least one other heart sound waveform. In thisexample, the particular heart sound includes at least a portion of oneof S1, S2, S3, and S4, and the first intra heart sound energy indicationand the corresponding first intra heart sound time indicationcorresponds to the at least a portion of one of S1, S2, S3, and S4,respectively.

In Example 2, the input circuit of Example 1 is optionally configured toreceive S2 information, and the heart sound recognition circuit isoptionally configured to recognize, within the S2 of the particularheart sound waveform, an intra S2 energy indication and a correspondingintra S2 time indication using the S2 information from the particularheart sound waveform and the S2 information from at least one otherheart sound waveform.

In Example 3, the heart sound waveform of Examples 1-2 optionallyincludes at least a portion of at least one physiological cycle.

In Example 4, the physiological cycle of Examples 1-3 optionallyincludes a cardiac cycle.

In Example 5, the particular heart sound of a particular heart soundwaveform of Examples 1-4 optionally includes an ensemble averaged heartsound over multiple physiological cycles.

In Example 6, the at least one other heart sound waveform of Examples1-5 optionally includes an immediately preceding heart sound waveform tothe particular heart sound waveform.

In Example 7, the heart sound recognition circuit of Examples 1-6 isoptionally configured to recognize the first intra heart sound energyindication and the corresponding first intra heart sound time indicationusing a heart sound template.

In Example 8, the heart sound template of Examples 1-7 optionallyincludes at least a portion of the heart sound information from the atleast one other heart sound waveform.

In Example 9, the heart sound recognition circuit of Examples 1-8 isoptionally configured to recognize the first intra heart sound energyindication and the corresponding first intra heart sound time indicationusing a cross correlation between at least a portion of the heart soundinformation from the particular heart sound waveform and at least aportion of the heart sound template.

In Example 10, the system of Examples 1-9 optionally includes animplantable medical device, including a heart sound sensor configured tosense a heart sound signal, and a heart sound feature detector, coupledto the heart sound sensor, the heart sound feature detector configuredto detect at least one heart sound feature using the heart sound signal.In this example, the heart sound information of Examples 1-9 optionallyincludes the at least one heart sound feature.

In Example 11, the heart sound recognition circuit of Examples 1-10optionally includes a detection circuit configured to: detect at leastone first candidate heart sound for the particular heart sound of the atleast one other heart sound waveform using the heart sound information,wherein the at least one first candidate heart sound includes an intraheart sound energy indication and a corresponding intra heart sound timeindication; and detect at least one second candidate heart sound for theparticular heart sound of the particular heart sound waveform using theheart sound information, wherein the at least one second candidate heartsound includes an intra heart sound energy indication and acorresponding intra heart sound time indication. In this example, theheart sound recognition circuit of Examples 1-10 is optionallyconfigured to recognize the first intra heart sound energy indicationand the corresponding first intra heart sound time indication using: theat least one detected first candidate heart sound; and the at least onedetected second candidate heart sound.

In Example 12, the at least one other heart sound waveform of Examples1-11 optionally includes an immediately preceding heart sound waveformto the particular heart sound waveform.

In Example 13, the heart sound recognition circuit of Examples 1-12optionally includes a cost analysis circuit, coupled to the detectioncircuit, the cost analysis circuit configured to calculate a cost forthe at least one second candidate heart sound, the calculated costincluding: a jump penalty indicative of a temporal cost associated withthe at least one second candidate heart sound; and a local scoreindicative of a local benefit associated with the at least one secondcandidate heart sound. In this example, the heart sound recognitioncircuit of Examples 1-12 is optionally configured to recognize the firstintra heart sound energy indication and the corresponding first intraheart sound time indication using the calculated cost.

In Example 14, the heart sound recognition circuit of Examples 1-13 isoptionally configured to calculate a back pointer that indicates apointer from the at least one second candidate heart sound to an optimalat least one first candidate heart sound using the cost analysis.

In Example 15, the heart sound recognition circuit of Examples 1-14optionally includes a coasting circuit, coupled to the heart soundrecognition circuit, configured to disregard the recognized first intraheart sound energy indication and the corresponding recognized firstintra heart sound time indication using a comparison of: the recognizedfirst intra heart sound energy indication and the correspondingrecognized first intra heart sound time indication; and at least oneother recognized intra heart sound energy indication and a correspondingat least one other recognized intra heart sound time indication withinthe particular heart sound of at least one other heart sound waveform.

In Example 16, the heart sound recognition circuit of Examples 1-15optionally includes a recapture circuit, coupled to the coastingcircuit, configured recapture the disregarded recognized first intraheart sound energy indication and the corresponding disregardedrecognized first intra heart sound time indication using a comparisonof: the disregarded recognized first intra heart sound energy indicationand the corresponding disregarded recognized first intra heart soundtime indication; and at least one other recognized intra heart soundenergy indication and a corresponding at least one other recognizedintra heart sound time indication within the particular heart sound ofat least one other heart sound waveform.

In Example 17, a system includes means for receiving heart soundinformation, such as by using an input circuit to receive heart soundinformation. The system also includes means for recognizing a firstintra heart sound energy indication and a corresponding first intraheart sound time indication within a particular heart sound of aparticular heart sound waveform using the heart sound information fromthe particular heart sound waveform and the heart sound information fromat least one other heart sound waveform, such as by using a heart soundrecognition circuit configured to recognize, within a particular heartsound of a particular heart sound waveform, a first intra heart soundenergy indication and a corresponding first intra heart sound timeindication using the heart sound information from the particular heartsound waveform and the heart sound information from at least one otherheart sound waveform.

In Example 18, the system of Example 17 optionally includes means fordisregarding the recognized first intra heart sound energy indicationand the corresponding recognized first intra heart sound timeindication, such as by using a coasting circuit configured to disregardthe recognized first intra heart sound energy indication and thecorresponding recognized first intra heart sound time indication using acomparison of: the recognized first intra heart sound energy indicationand the corresponding recognized first intra heart sound timeindication; and at least one other recognized intra heart sound energyindication and a corresponding at least one other recognized intra heartsound time indication within the particular heart sound of at least oneother heart sound waveform.

In Example 19, the system of examples 17-18 optionally includes meansfor recapturing the disregarded recognized first intra heart soundenergy indication and the corresponding disregarded recognized firstintra heart sound time indication, such as by using a recapture circuitconfigured recapture the disregarded recognized first intra heart soundenergy indication and the corresponding disregarded recognized firstintra heart sound time indication using a comparison of: the disregardedrecognized first intra heart sound energy indication and thecorresponding disregarded recognized first intra heart sound timeindication; and at least one other recognized intra heart sound energyindication and a corresponding at least one other recognized intra heartsound time indication within the particular heart sound of at least oneother heart sound waveform.

In Example 20, a method includes receiving heart sound information. Themethod also includes recognizing a first intra heart sound energyindication and a corresponding first intra heart sound time indicationwithin a particular heart sound of a particular heart sound waveformusing the heart sound information from the particular heart soundwaveform and the heart sound information from at least one other heartsound waveform. In this example, the recognizing the first intra heartsound energy indication and the corresponding first intra heart soundtime indication within the particular heart sound includes recognizingwithin at least a portion of one of S1, S2, S3, and S4, and therecognizing the first intra heart sound energy indication and thecorresponding first intra heart sound time indication corresponds to theat least a portion of one of S1, S2, S3, and S4, respectively.

In Example 21, the receiving the heart sound information of Example 20optionally includes receiving S2 information, and the recognizing thefirst intra heart sound energy indication and the corresponding firstintra heart sound time indication within the particular heart sound ofthe particular heart sound waveform of Example 20 optionally includesrecognizing an intra S2 energy indication and a corresponding intra S2time indication within an S2 of the particular heart sound waveform. Inthis example, the using the heart sound information from the particularheart sound waveform and the heart sound information from the at leastone other heart sound waveform of Example 20 optionally includes usingthe S2 information from the particular heart sound waveform and the S2information from at least one other heart sound waveform.

In Example 22, the heart sound waveform of Examples 20-21 optionallyincludes at least a portion of at least one physiological cycle.

In Example 23, the physiological cycle of Examples 20-22 optionallyincludes a cardiac cycle.

In Example 24, the particular heart sound of the particular heart soundwaveform of Examples 20-23 optionally includes an ensemble averagedheart sound over multiple physiological cycles.

In Example 25, the using the heart sound information from the at leastone other heart sound waveform of Examples 20-24 optionally includesusing the heart sound information from an immediately preceding heartsound waveform to the particular heart sound waveform.

In Example 26, the recognizing the first intra heart sound energyindication and the corresponding first intra heart sound time indicationof Examples 20-25 optionally includes using a heart sound template andcomparing the heart sound information from the particular heart soundwaveform to the heart sound template.

In Example 27, the using the heart sound template of Examples 20-26optionally includes updating the heart sound template using at least aportion of the heart sound information from the at least one other heartsound waveform.

In Example 28, the recognizing the first intra heart sound energyindication and the corresponding first intra heart sound time indicationof Examples 20-27 optionally includes cross correlating between at leasta portion of the heart sound information from the particular heart soundwaveform and at least a portion of the heart sound template.

In Example 29, the method of Examples 20-28 optionally includesimplantably sensing a heart sound signal and implantably detecting atleast one heart sound feature using the heart sound signal. In thisexample, the using the heart sound information of Examples 20-28optionally includes using the at least one heart sound feature.

In Example 30, the method of Examples 20-29 optionally includesdetecting at least one first candidate heart sound for the particularheart sound of the at least one other heart sound waveform using theheart sound information, wherein detecting the at least one firstcandidate heart sound includes detecting an intra heart sound energyindication and a corresponding intra heart sound time indication, anddetecting at least one second candidate heart sound for the particularheart sound of the particular heart sound waveform using the heart soundinformation, wherein detecting the at least one second candidate heartsound includes detecting an intra heart sound energy indication and acorresponding intra heart sound time indication. In this example, therecognizing the first intra heart sound energy indication and thecorresponding first intra heart sound time indication of Examples 20-29optionally includes using: the at least one detected first candidateheart sound; and the at least one detected second candidate heart sound.

In Example 31, the recognizing the at least one first candidate heartsound for the particular heart sound of the at least one other heartsound waveform of Examples 20-30 optionally includes recognizing the atleast one first candidate heart sound for the particular heart sound ofan immediately preceding heart sound waveform to the particular heartsound waveform.

In Example 32, the method of Examples 20-31 optionally includescalculating a cost for the at least one second candidate heart sound,including: calculating a jump penalty indicative of a temporal costassociated with the at least one second candidate heart sound; andcalculating a local score indicative of a local benefit associated withthe at least one second candidate heart sound. In this example, therecognizing the first intra heart sound energy indication and thecorresponding first intra heart sound time indication of Examples 20-31optionally includes using the calculated cost.

In Example 33, the method of Examples 20-32 optionally includescalculating a back pointer that indicates a pointer from the at leastone second candidate heart sound to an optimal at least one firstcandidate heart sound using the cost analysis.

In Example 34, the method of Examples 20-33 optionally includesdisregarding the recognized first intra heart sound energy indicationand the corresponding recognized first intra heart sound time indicationusing a comparison of: the recognized first intra heart sound energyindication and the corresponding recognized first intra heart sound timeindication; and at least one other recognized intra heart sound energyindication and a corresponding at least one other recognized intra heartsound time indication within the particular heart sound of at least oneother heart sound waveform.

In Example 35, the method of Examples 20-34 optionally includesrecapturing the disregarded recognized first intra heart sound energyindication and the corresponding disregarded recognized first intraheart sound time indication using a comparison of: the disregardedrecognized first intra heart sound energy indication and thecorresponding disregarded recognized first intra heart sound timeindication; and at least one other recognized intra heart sound energyindication and a corresponding at least one other recognized intra heartsound time indication within the particular heart sound of at least oneother heart sound waveform.

This overview is intended to provide an overview of the subject matterof the present patent application. It is not intended to provide anexclusive or exhaustive explanation of the invention. The detaileddescription is included to provide further information about the subjectmatter of the present patent application.

BRIEF DESCRIPTION OF THE DRAWINGS

In the drawings, which are not necessarily drawn to scale, like numeralsdescribe substantially similar components throughout the several views.Like numerals having different letter suffixes represent differentinstances of substantially similar components. The drawings illustrategenerally, by way of example, but not by way of limitation, variousembodiments discussed in the present document.

FIG. 1 illustrates generally an example of an illustration of portionsof a heart sound signal including S1 and S2.

FIG. 2 illustrates generally an example of a system including an inputcircuit and a heart sound recognition circuit.

FIG. 3 illustrates generally an example of portions of a systemincluding an implantable medical device, the implantable medical deviceincluding a heart sound sensor and a heart sound feature detector.

FIG. 4 illustrates generally an example of portions of a systemincluding a heart sound recognition circuit, the heart sound recognitioncircuit including a detection circuit and a cost analysis circuit.

FIG. 5 illustrates generally an example of portions of a systemincluding a heart sound recognition circuit, the heart sound recognitioncircuit including a coasting circuit and a recapture circuit.

FIG. 6A illustrates generally an example of a relationship betweenmultiple candidate heart sounds from multiple heart sound waveforms.

FIG. 6B illustrates generally an example of an illustration including aheart sound signal and multiple heart sound candidates.

FIG. 6C illustrates generally a diagram including a heart sound waveformand exemplary heart sound waveforms.

FIG. 7 illustrates generally an example of a method including receivingheart sound information and recognizing a first intra heart sound energyindication and a corresponding first intra hear sound time indicationwithin a particular heart sound of a particular heart sound waveform.

FIG. 8 illustrates generally an example of portions of a methodincluding implantably sensing a heart sound signal and implantablydetecting at least one heart sound feature.

FIG. 9 illustrates generally an example of portions of a methodincluding detecting at least one candidate heart sound for theparticular heart sound of the particular heart sound waveform and the atleast one other heart sound waveform.

FIG. 10 illustrates generally an example of portions of a methodincluding calculating a cost for at least one candidate heart sound andrecognizing the first intra heart sound energy indication and thecorresponding first intra heart sound time indication using thecalculated cost.

FIG. 11 illustrates generally an example of portions of a methodincluding calculating a back pointer.

FIG. 12 illustrates generally an example of portions of a methodincluding disregarding the recognized first intra heart sound energyindication and the corresponding recognized first intra heart sound timeindication and recapturing the disregarded recognized first intra heartsound energy indication and the corresponding disregarded recognizedfirst intra heart sound time indication.

FIG. 13 illustrates generally an example of a system including animplantable medical device, an input circuit, and a heart soundrecognition circuit. The implantable medical device includes a heartsound sensor and a heart sound feature detector.

DETAILED DESCRIPTION

The following detailed description includes references to theaccompanying drawings, which form a part of the detailed description.The drawings show, by way of illustration, specific embodiments in whichthe invention may be practiced. These embodiments, which are alsoreferred to herein as “examples,” are described in enough detail toenable those skilled in the art to practice the invention. Theembodiments may be combined, other embodiments may be utilized, orstructural, logical and electrical changes may be made without departingfrom the scope of the present invention. The following detaileddescription is, therefore, not to be taken in a limiting sense, and thescope of the present invention is defined by the appended claims andtheir equivalents.

In this document, the terms “a” or “an” are used, as is common in patentdocuments, to include one or more than one. In this document, the term“or” is used to refer to a nonexclusive or, such that “A or B” includes“A but not B.” “B but not A,” and “A and B,” unless otherwise indicated.Furthermore, all publications, patents, and patent documents referred toin this document are incorporated by reference herein in their entirety,as though individually incorporated by reference. In the event ofinconsistent usages between this document and those documents soincorporated by reference, the usage in the incorporated reference(s)should be considered supplementary to that of this document; forirreconcilable inconsistencies, the usage in this document controls.

Heart sounds include S1 (or the “first heart sound”), S2 (or “the secondheart sound”), S3 (or “the third heart sound”), S4 (or “the fourth heartsound”), and their various sub-components. S1 is believed to beindicative of, among other things, mitral valve closure, tricuspid valveclosure, and aortic valve opening. S2 is believed to be indicative of,among other things, aortic valve closure and pulmonary valve closure. S3is believed to be a ventricular diastolic filling sound often indicativeof certain pathological conditions, including heart failure. S4 isbelieved to be a ventricular diastolic filling sound resulted fromatrial contraction and is believed usually indicative of pathologicalconditions. The term “heart sound” hereinafter refers to any indicationof a heart sound (e.g., S1, S2, etc.) or any component thereof (e.g., M1component of S1 (indicative of mitral valve closure), A2 component of S2(indicative of aortic valve closure), P2 component of S2 (indicative ofpulmonic valve closure), etc.).

A heart sound can include audible or inaudible mechanical vibrationscaused by cardiac activity. In certain examples, heart sounds can besensed with an accelerometer. Such mechanical vibrations can beconceptualized as providing acoustic energy.

The present inventors have recognized, among other things, that themaximum amplitude of a heart sound signal may not be the most desirableidentifier of the heart sound. For example, a first intra heart soundenergy indication and a corresponding first intra heart sound timeindication for a particular heart sound of a particular heart soundwaveform can be recognized, such as by using heart sound informationfrom multiple heart sound waveforms. In an example, the first intraheart sound energy indication and the corresponding first intra heartsound time indication can be recognized using the heart soundinformation from the particular heart sound waveform and the heart soundinformation from at least one other heart sound waveform. The recognizedfirst intra heart sound energy indication and the correspondingrecognized first intra heart sound time indication can be indicative orcharacteristic of a desirable heart sound amplitude and timing withinthe particular heart sound waveform.

FIG. 1 illustrates generally an example of an illustration 100 includingportions of a heart sound signal 115, including S1 120 and S2 125, shownwith respect to Amplitude (mG) 110 and Time (msec) 105, where mG areunits of acceleration that are produced when an accelerometer is used tomeasure the vibrations produced by the heart sounds.

A heart sound signal can include multiple peaks. In this example, the S1120 portion of the heart sound signal 115 has multiple peaks, such aspeak 121, peak 122, and peak 123, and the S2 125 portion of the heartsound signal 115 has multiple peaks, such as peak 126 and peak 127. Inan example, the timing and amplitude of S1 can be determined using theinformation from the current S1, such as by selecting the largestamplitude in the S1 120 portion of the heart sound signal 115 and itscorresponding timing. However, the present inventors have recognized,among other things, that the peak having the largest amplitude may notbe the best identifier of the heart sound. In certain examples, a moredesirable heart sound identifier can be attained using the informationfrom the current S1, as well as information from an S1 of another heartsound cycle. In certain examples, the largest amplitude in a heart soundsignal can include noise or other undesirable artifacts, or the largestamplitude may be an anomaly. In certain instances, the anomaly maycontain valuable information. However, in other instances, the anomalycan undesirably influence the overall heart sound data. Thus, in certainexamples, peak 121 or peak 123 and their corresponding timings could bea more desirable identifier for the S1 120 portion of the heart soundsignal 115.

FIG. 2 illustrates generally an example of a system 200 including aninput circuit 205 and a heart sound recognition circuit 210. The inputcircuit 205 can be configured to receive heart sound information. Theheart sound recognition circuit 210 can be configured to recognize,within a particular heart sound of a particular heart sound waveform, afirst intra heart sound energy indication and a corresponding firstintra heart sound time indication. In an example, the heart soundrecognition circuit 210 can recognize the first intra heart sound energyindication and the corresponding first intra heart sound timeindication, such as by using the heart sound information from theparticular heart sound waveform and the heart sound information from atleast one other heart sound waveform.

In certain examples, the input circuit 205 can be configured to receiveheart sound information from a heart sound sensor or other sensorconfigured to sense, detect, or otherwise collect heart soundinformation. In certain examples, the input circuit 205 can beconfigured to receive heart sound information from another device, suchas an external programmer, a memory, or other device capable of havingheart sound information.

The heart sound information can include any information indicative of aheart sound (e.g., the acoustic or mechanical energy of a heart). Incertain examples, the heart sound information can include at least aportion of at least one heart sound signal, such as an entire heartsound signal, features of a heart sound signal, or multiple heart soundsignals. The heart sound information can include at least a portion ofS1 information, S2 information, S3 information, S4 information, or otherheart sound information.

In this example, the heart sound recognition circuit 210 can be coupledto the input circuit 205. The heart sound recognition circuit 210 can beconfigured to receive information (e.g., heart sound information) fromthe input circuit 205. In certain examples, the heart sound recognitioncircuit 210 can include the input circuit 205, or the heart soundrecognition circuit 210 or the input circuit 205 can be implementedusing a processor, a programmer, controller, or the like.

In an example, the particular heart sound can include at least one ofS1, S2, S3, S4, or other portions or components of a heart sound signal.Further, the particular heart sound can include at least a portion ofone of S1, S2, S3, S4, or other portions or components of a heart soundsignal, such as at least a portion of S1, the aortic valve component ofS2 (commonly referred to as the A2 component of S2), the pulmonic valvecomponent of S2 (commonly referred to as the P2 component of S2), etc.

In an example, the heart sound waveform can include at least a portionof at least one physiological cycle. Generally, the body functions inphysiological cycles. In certain examples, a physiological cycle caninclude a cardiac cycle, a respiration cycle, or other physiologicalcycle of the body. The physiological cycle can be detected using anelectrical signal (e.g., an electrocardiogram (ECG) or an impedancesignal indicative of cardiac or respiratory activity), or thephysiologic cycle can be detected using other signals, such as by usinga mechanical signal (e.g., a pressure signal indicative of cardiac orrespiratory activity or a heart sound signal indicative of cardiacactivity). In an example, the heart sound waveform can include at leasta portion of at least one physiological cycle, such as a portion of thecardiac cycle or a portion of the respiration cycle. In other examples,the heart sound waveform can include multiple physiological cycles, suchas multiple cardiac cycles. In other examples, the heart sound waveformcan include a specified time period, such as a 10-minute time period, orother time period.

In an example, the particular heart sound of the particular heart soundwaveform can include an ensemble average of the particular heart soundover a heart sound waveform, such as that disclosed in the commonlyassigned Siejko et al. U.S. Pat. No. 7,115,096 entitled “THIRD HEARTSOUND ACTIVITY INDEX FOR HEART FAILURE MONITORING,” which is herebyincorporated by reference in its entirety, including its disclosure ofensemble averaging an acoustic signal. In certain examples, the ensembleaverage of the particular heart sound over multiple heart soundwaveforms can include at least a portion of the S1 (or at least aportion of an other heart sound, such as S2, S3, S4, etc.) over a heartsound waveform, such as over multiple physiological cycles (e.g.,multiple cardiac cycles) or over a specified time period (e.g., 1minute, 10 minutes, 1 hour, 1 day, etc.).

In the example of FIG. 2, the first intra heart sound energy indicationand the corresponding first intra heart sound time indication can beindicative of a desirable heart sound amplitude and timing within theparticular heart sound waveform. In certain examples, the desirableheart sound amplitude and timing can include a combination of the heartsound amplitude having the largest or most consistent peak,peak-to-peak, peak-to-peak with zero-crossing, or other heart soundamplitude within the particular heart sound waveform, coupled with theheart sound timing having the most consistent timing of the heart soundamplitude events (e.g., the peak, peak-to-peak, peak-to-peak withzero-crossing, or other heart sound amplitude within the particularheart sound waveform).

In an example, the first intra heart sound energy indication can includean energy (e.g., an amplitude) within the particular heart soundwaveform (e.g., within the S1, S2, etc.). Similarly, the correspondingfirst intra heart sound time indication can include a time within theparticular heart sound waveform (e.g., within the S1, S2, etc.). Incertain examples, the first intra heart sound time can include the timeassociated with the first intra heart sound amplitude, or the firstintra heart sound time can include a time different or independent fromthe first intra heart sound amplitude.

In an example, the particular heart sound waveform can include a currentheart sound waveform. In certain examples, the system 200 can beconfigured to operate in real-time, or the system 200 can be configuredto operate using stored data (e.g., stored or buffered heart soundinformation). In certain examples, the at least one other heart soundwaveform can include at least one heart sound waveform occurringprevious to, occurring after, or occurring at a combination of previousto or after the particular heart sound waveform. In an example, the atleast one other heart sound waveform can include the immediatelypreceding heart sound waveform to the particular heart sound waveform.

For example, in the example of FIG. 6A, four heart sound waveforms aredisplayed: a first heart sound waveform 610, a second heart soundwaveform 620, a third heart sound waveform 630, and a fourth heart soundwaveform 640. In an example, the particular heart sound waveform caninclude the third heart sound waveform 630. In this example, the atleast one other heart sound waveform can include at least one of thefirst heart sound waveform 610, the second heart sound waveform 620, andthe fourth heart sound waveform 640.

In an example, the input circuit 205 can be configured to receive S2information. The heart sound recognition circuit 210 can be configuredto recognize an intra S2 energy indication and a corresponding intra S2time indication within the S2 of the particular heart sound waveform. Inan example, the heart sound recognition circuit 210 can be configured torecognize the intra S2 energy indication and the corresponding intra S2time indication using the S2 information from the particular heart soundwaveform and also using the S2 information from at least one other heartsound waveform.

In an example, the heart sound recognition circuit 210 can be configuredto recognize the first intra heart sound energy indication and thecorresponding first intra heart sound time indication using a heartsound template, such as by comparing the heart sound information fromthe particular heart sound waveform to the heart sound template. In anexample, the heart sound information can include at least one heartsound feature, such as a morphological feature. Thus, the first intraheart sound energy indication and the corresponding first intra heartsound time indication can be recognized by comparing at least one heartsound feature, such as a morphological feature, of the heart soundinformation from the particular heart sound waveform to the heart soundtemplate.

In certain examples, a heart sound template can include previouslyattained heart sound information from a subject (e.g., a subject onwhich system 200 is configured to perform) or a population (e.g., one ormore other subjects, such as subjects having normal cardiac health,subjects having a specific physiological condition, etc.). In anexample, the heart sound information can include at least one heartsound feature, such as a morphological feature. In an example, thepreviously attained heart sound information can include at least aportion of the heart sound information from the at least one other heartsound waveform of the subject. In certain examples, the previouslyattained heart sound information can include heart sound informationfrom a heart sound waveform that occurs previous to the particular heartsound. In certain examples, the previously attained heart soundinformation can include heart sound information from a heart soundwaveform that occurs later in time than the particular heart soundwaveform, such as when the heart sound recognition circuit 210 isrecognizing using stored or buffered heart sound information.

In an example, the heart sound template can be updated using the heartsound information from the subject, such as the heart sound informationfrom the particular heart sound waveform or the heart sound informationfrom the at least one other heart sound waveform.

Further, in certain examples of FIG. 2, the heart sound recognitioncircuit 210 can be configured to recognize the first intra heart soundenergy indication or the corresponding first intra heart sound timeindication using a cross correlation between (1) at least a portion ofthe heart sound information from the particular heart sound waveform,such as at least one heart sound feature (e.g., at least onemorphological feature), and (2) at least a portion of the heart soundtemplate.

In an example, the heart sound recognition circuit 210 can be configuredto produce at least one table. The table can include the recognizedintra heart sound energy indication and the corresponding first intraheart sound time indication. In an example, the table can be stored inmemory, and can provide a compact representation of heart soundinformation.

FIG. 3 illustrates generally an example of portions of a system 300including an implantable medical device 215 including a heart soundsensor 220 and a heart sound feature detector 225.

In this example, the heart sound sensor 220 can be configured to sense aheart sound signal of a subject. The heart sound signal can include anysignal that includes an indication of at least a portion of the at leastone heart sound of the subject (e.g. S1, S2, S3, S4, or any componentsthereof, such as A2, P2, etc.). The heart sound sensor 220 can beconfigured to produce a heart sound signal, such as an electrical oroptical representation of a heart sound signal, that includesinformation about the acoustic or vibrational heart sound signal of thesubject. The heart sound sensor 220 can include any device configured tosense the heart sound signal of the subject. In certain examples, theheart sound sensor 220 can include an implantable sensor including atleast one of an accelerometer, an acoustic sensor, a microphone, etc.

In an example, the heart sound sensor 220 can include an accelerometerconfigured to sense an acceleration signal indicative of the heart soundof the subject, such as that disclosed in the commonly assigned Carlsonet al. U.S. Pat. No. 5,792,195 entitled “ACCELERATION SENSED SAFE UPPERRATE ENVELOPE FOR CALCULATING THE HEMODYNAMIC UPPER RATE LIMIT FOR ARATE ADAPTIVE CARDIAC RHYTHM MANAGEMENT DEVICE,” which is herebyincorporated by reference in its entirety including its disclosure ofaccelerometer detection of heart sounds, or such as that disclosed inthe commonly assigned Siejko et al. U.S. patent application Ser. No.10/334,694, entitled “METHOD AND APPARATUS FOR MONITORING OF DIASTOLICHEMODYNAMICS,” filed Dec. 30, 2002 (Attorney Docket No. 279.576US1)(herein “Siejko et al. '694”), which is hereby incorporated by referencein its entirety including its disclosure of accelerometer detection ofheart sounds. In other examples, other accelerometer or accelerationsensor configurations can be used to sense the heart sound signal.

In another example, the heart sound sensor 220 can include an acousticsensor configured to sense an acoustic energy indicative of the heartsound of the subject, such as that disclosed in the commonly assignedSiejko et al. '694, incorporated by reference in its entirety. In otherexamples, other acoustic sensor or microphone configurations can be usedto sense the heart sound signal.

In the example of FIG. 3, the heart sound feature detector 225 iscoupled to the heart sound sensor 220. The heart sound feature detector225 can be configured to receive the heart sound signal from the heartsound sensor 220. The heart sound feature detector 225 can be configuredto detect at least one feature of at least a portion of at least oneheart sound. The heart sound feature can include at least onemeasurement, characteristic, morphology, computation, or interval of atleast a portion of at least one heart sound. In certain examples, thisincludes at least one of an amplitude of a heart sound signal, amagnitude of a heart sound signal, a total energy of a heart soundsignal, a peak of a heart sound signal, etc. (e.g., an amplitude ormagnitude of at least one peak, at least one valley, or at least oneother portion of an S1, an amplitude or magnitude of at least one peak,at least one valley, or at least one other portion of an S2, etc.).

In an example, the heart sound information used by the heart soundrecognition circuit 210 can include the detected at least one heartsound feature. In certain examples, the heart sound sensor 220 caninclude the heart sound feature detector 225, or the heart sound featuredetector 225 can include the heart sound sensor 220.

FIG. 4 illustrates generally an example of portions of a system 400including a heart sound recognition circuit 210, the heart soundrecognition circuit 210 including a detection circuit 230 and a costanalysis circuit 235.

In an example, the detection circuit 230 can be configured to detect atleast one first candidate heart sound for the particular heart sound ofthe at least one other heart sound waveform. In an example, thedetection circuit 230 can detect the at least one first candidate heartsound using the heart sound information. The at least one firstcandidate heart sound can include an intra heart sound energy indicationand a corresponding intra heart sound time indication. In an example,the candidate heart sound can be identified or characterized, such as byusing the intra heart sound energy indication and the correspondingintra heart sound time indication. A candidate heart sound can includeany portion, component, or identifier of the heart sound signal, theheart sound information, or the at least one heart sound feature for aheart sound of a heart sound waveform. In an example, the firstcandidate heart sound can include at least one feature (e.g., a positivepeak, a negative peak, etc.) of the particular heart sound of the atleast one other heart sound waveform, the at least one feature having anintra heart sound energy indication associated with the at least onefeature (e.g., the amplitude of the positive peak, the amplitude of thenegative peak, etc.) and a corresponding intra heart sound timeindication associated with the at least one feature.

In an example, the detection circuit 230 can be configured to detect atleast one second candidate heart sound for the particular heart sound ofthe particular heart sound waveform. In an example, the detectioncircuit 230 can detect the at least one second candidate heart soundusing the heart sound information. The at least one second candidateheart sound can include an intra heart sound energy indication and acorresponding intra heart sound time indication. In an example, thecandidate heart sound can be identified or characterized using the intraheart sound energy indication and the corresponding intra heart soundtime indication. In an example, the second candidate heart sound caninclude at least one feature (e.g., a positive peak, a negative peak,etc.) of the particular heart sound of the particular heart soundwaveform, the at least one feature having an intra heart sound energyindication associated with the at least one feature (e.g., the amplitudeof the positive peak, the amplitude of the negative peak, etc.) and acorresponding intra heart sound time indication associated with the atleast one feature.

In the example of FIG. 4, the heart sound recognition circuit 210 can beconfigured to recognize the first intra heart sound energy indicationand the corresponding first intra heart sound time indication using theat least one detected first candidate heart sound and the at least onedetected second candidate heart sound. The first intra heart soundenergy indication and the corresponding first intra heart sound timeindication can be recognized using a relationship between the at leastone detected first candidate heart sound and the at least one detectedsecond candidate heart sound, such as by calculating a cost from the atleast one detected first candidate heart sound to the at least onedetected second candidate heart sound.

In an example, the cost analysis circuit 235 can be coupled to thedetection circuit 230. The cost analysis circuit 235 can be configuredto use a dynamic programming method, such as a Viterbi method or otherdynamic programming method, to determine a desirable heart soundcandidate for the particular heart sound waveform. In an example, thedesirable heart sound candidate can include a candidate having the leastcost. For example, by selecting “desirable” heart sound indications fromamong multiple candidates, in a manner that tends to reduce or minimizesthe cost function over many cardiac cycles, the present methods can beused to track the more desirable heart sound indications

In an example, the cost analysis circuit 235 can be configured tocalculate a cost for each second candidate heart sound. In an example,the cost can be calculated for the second candidate heart sound using atleast one of a jump penalty and a local score. For example, the jumppenalty can include a temporal cost associated with the second candidateheart sound. In an example, the temporal cost can include a timedifference between the second candidate heart sound and a firstcandidate heart sound (see, e.g., FIG. 6). The local score can include alocal benefit associated with the at least one second candidate heartsound. In an example, the local score includes the amplitude of thesecond heart sound candidate. In an example, the local score or the jumppenalty can be weighted (e.g., by multiplying the local score or thejump penalty by a scaling factor) to further tailor the cost analysis.

In an example, the heart sound recognition circuit 210 can be configuredto recognize the first intra heart sound energy indication and thecorresponding first intra heart sound time indication using thecalculated cost, such as by selecting the heart sound candidate for theparticular heart sound waveform having a lowest cost or a highestbenefit.

In an example, the cost analysis can include a total score. The totalscore can factor in at least one of the jump penalty for a candidateheart sound having a temporal cost and the local score for the candidateheart sound having a local benefit. In an example, the total score(“D(t, x)”) can be calculated by taking the difference of the jumppenalty (“J(x′, x)”) from a previous total score (“D(t−1, x′)”), and byadding the local score (“d(X_(t), x)”) to the maximum result of thedifference:

$\begin{matrix}{{{D\left( {t,x} \right)} = {{\max\limits_{x^{\prime} \in {M{(x)}}}\left\{ {{D\left( {{t - 1},x^{\prime}} \right)} - {J\left( {x^{\prime},x} \right)}} \right\}} + {d\left( {X_{t},x} \right)}}},} & \left( {{Eq}.\mspace{14mu} 1} \right)\end{matrix}$

wherein t denotes a heart sound waveform, x denotes a candidate heartsound, and M(x) includes a set of possible predecessors of x.

In an example, the heart sound recognition circuit 210 can be configuredto calculate a back pointer. In an example, the back pointer canindicate a pointer from the at least one second candidate heart sound toa desirable at least one first candidate heart sound. The desirable atleast one first candidate heart sound typically includes the firstcandidate heart sound having a maximum result of the difference betweenthe previous total score and the current jump penalty. Thus, in anexample, the back pointer (“B(t, x)”) can be calculated using:

$\begin{matrix}{{B\left( {t,x} \right)} = {\underset{x^{\prime} \in {M{(x)}}}{\arg \; \max}{\left\{ {{D\left( {{t - 1},x^{\prime}} \right)} - {J\left( {x^{\prime},x} \right)}} \right\}.}}} & \left( {{Eq}.\mspace{14mu} 2} \right)\end{matrix}$

FIG. 5 illustrates generally an example of portions of a system 500including a heart sound recognition circuit 210 including a coastingcircuit 240 and, if desired, also including a recapture circuit 245.

In an example, the coasting circuit 240 can be coupled to the heartsound recognition circuit 210. The coasting circuit 240 can beconfigured to disregard the recognized first intra heart sound energyindication and the corresponding recognized first intra heart sound timeindication. In an example, if the calculated cost of a recognized firstintra heart sound energy indication and corresponding first intra heartsound time indication is too high (e.g., above a threshold, or aboveprevious results), or if the total score of the recognized first intraheart sound energy indication and corresponding first intra heart soundtime indication is too low (e.g., below a threshold, or below previousresults), then the coasting circuit 240 can be configured to disregardthe recognized first intra heart sound energy indication andcorresponding first intra heart sound time indication.

The coasting circuit 240 can be configured to coast (e.g., disregardheart sound indications that would otherwise be recognized) for acertain period (e.g., a certain number of heart sound waveforms, acertain period of time, etc.). In an example, if, at the end of thecertain period, the calculated cost remains too high, or if the totalscore remains too low, the coasting circuit 240 will stop coasting, ifso configured. Generally, if the end of the certain period is reachedwith the calculated cost still too high, or the total score still toolow, this can be an indication that the heart sound information haschanged or a problem has arisen (e.g., noise, physical condition change,system failure, etc.). In an example, if the calculated cost remains toohigh, or if the total score remains too low, at the end of the certainperiod the coasting circuit 240 can provide a notification to a user, ifso configured, such as by using a notification circuit.

In an example, the coasting circuit 240 can be configured to disregardthe recognized first intra heart sound energy indication and thecorresponding recognized first intra heart sound time indication basedupon a result of a comparison. In an example, the comparison can includea comparison of the recognized first intra heart sound energy indicationand the corresponding recognized first intra heart sound time indicationand at least one other recognized intra heart sound energy indicationand a corresponding at least one other recognized intra heart sound timeindication within the particular heart sound of at least one other heartsound waveform.

In an example, the recapture circuit 245 can be coupled to the coastingcircuit 240 to provide a storage buffer for the disregarded informationbefore discarding, so that it can be recaptured, if desired. Generally,the recapture circuit 245 can be configured to recapture the disregardedrecognized first intra heart sound energy indication and thecorresponding disregarded recognized first intra heart sound timeindication. In an example, if a recognized first intra heart soundenergy indication and a corresponding recognized first intra heart soundtime indication have been disregarded, such as by using the coastingcircuit 240, and the coasting circuit 240 recurrently reaches the end ofthe certain period, then it may be beneficial to recapture thedisregarded recognized first intra heart sound energy indication and thecorresponding recognized first intra heart sound time indication (e.g.,it may be beneficial if the heart sound information has changed, if thesubject's status has changed, etc.).

In an example, the recapture circuit 245 can be configured to recapturethe disregarded recognized first intra heart sound energy indication andthe corresponding disregarded recognized first intra heart sound timeindication, with the recapture triggered using a comparison. In anexample, the comparison can include a comparison of the disregardedrecognized first intra heart sound energy indication and thecorresponding disregarded recognized first intra heart sound timeindication and at least one other recognized intra heart sound energyindication and a corresponding at least one other recognized intra heartsound time indication within the particular heart sound of at least oneother heart sound waveform.

FIG. 6A illustrates generally an example, using exemplary data, of arelationship 600 between multiple candidate heart sounds 611, 612, 621,622, 631, 632, 633, 641, 642 from multiple heart sound waveforms (thefirst heart sound waveform 610, the second heart sound waveform 620, thethird heart sound waveform 630, and the fourth heart sound waveform640), shown with respect to candidates 601 and heart sound waveform 602.In this example, the candidate heart sound 611 can be identified ascandidate heart sound (1,1) 611, where (1,1) refers to (heart soundwaveform, candidate number of the heart sound waveform). Each candidateheart sound (e.g., candidate heart sound (1,1) 611) is shown with itsamplitude (rounded up to the nearest whole number) and correspondingtime (e.g., candidate heart sound (1,1) 611 has a rounded amplitude of 5and a corresponding time index of 265, (5,265)).

The relationship 600 illustrates an example of four heart soundwaveforms, each having at least two candidate heart sounds. In anexample, Table 1 (below) generally illustrates examples of calculatedjump penalties associated with each candidate. In this example, the jumppenalty is indicative of the temporal distance between a heart soundcandidate of a particular heart sound waveform (e.g., the second heartsound waveform 620) and a heart sound candidate of the immediatelypreceding heart sound waveform to the particular heart sound waveform(e.g., the first heart sound waveform 610).

TABLE 1 J = jump penalty (HSW, Candidate) 1 2 3 1 0 0 2 1, 17 22, 4 312, 33 0, 21 9, 12 4 25, 13, 4 37, 25, 16

In Table 1, the candidate heart sound (1,1) 611 and the candidate heartsound (1,2) 612 are initially given jump penalties of zero, becausethere is no data preceding them. Further, relationship 600 shows jumppaths 645, 646. The jump path 645 is a jump path from the candidateheart sound (1,1) 611 to the candidate heart sound (2,2) 622. In Table1, the jump path 645 is displayed in row 2, column 2, having a value of22, which is representative of a shift in the time index from 265 to287. The jump path 646 is a jump path from the candidate heart sound(1,2) 612 to the candidate heart sound (2,2) 622

In an example, Table 2 (below) generally illustrates the calculatedtotal scores associated with each candidate of relationship 600 inaccordance with Eq. 1, where the local score (“d(X_(t),x)”) includes theamplitude of the candidate and a gain. In this example, the gain of thelocal score is 5.

TABLE 2${D\left( {t,x} \right)} = {{\max\limits_{x^{\prime} \in {M{(x)}}}\left\{ {{D\left( {{t - 1},x^{\prime}} \right)} - {J\left( {x^{\prime},x} \right)}} \right\}} + {d\left( {X_{t},x} \right)}}$(HSW, Candidate) 1 2 3 1 0 0 2 39 21 3 82 69 55 4 92 60

In an example, Table 3 (below) generally illustrates the calculated backpointer for each candidate of relationship 600 in accordance with Eq. 2.

TABLE 3${B\left( {t,x} \right)} = \underset{x^{\prime} \in {M{(x)}}}{\arg \mspace{11mu} \max}\left\{ {{D\left( {{t - 1},x^{\prime}} \right)} - {J\left( {x^{\prime},x} \right)}} \right\}$(HSW, Candidate) 1 2 3 1 0 0 2 1 2 3 1 1 1 4 1 1

FIG. 6A also includes a traceback path 647. In an example, the tracebackpath 647 can be determined using the calculated back pack pointers. Inan example, a candidate was chosen at the fourth heart sound waveform640, such as by choosing the candidate having the highest total score.In this example, the candidate heart sound (4,1) 641 was chosen to startthe traceback path. The traceback path goes to the first candidate ofthe previous heart sound waveform, the candidate heart sound (3,1) 631,using the back pointer calculated for the candidate heart sound (4,1)641, 1. Similarly, the traceback path continues to the first candidateof the second heart sound waveform, the candidate heart sound (2,1) 621,using the back pointer calculated for the candidate heart sound (3,1)631, 1, and so on.

FIG. 6B illustrates generally an example of an illustration 650including a heart sound signal 655, shown with respect to Amplitude (mG)652 and Time (msec) 651, and including multiple heart sound candidates.In this example, the multiple heart sound candidates include a first S1candidate 660, a second S1 candidate 661, a third S1 candidate 662, afirst S2 candidate 663, and a second S2 candidate 664.

In an example, the at least one first candidate heart sound for theparticular heart sound of the at least one particular heart soundwaveform can include (1) (for the S1 of the current heart sound cycleshown in the illustration 650) the first S1 candidate 660, the second S1candidate 661, and the third S1 candidate 662, or (2) (for the S2 of thecurrent heart sound cycle shown in the illustration 650) the first S2candidate 663 and the second S2 candidate 664.

For example, in a relationship similar to the relationship 600 of FIG.6A showing S1 candidates with respect to heart sound waveforms, wherethe heart sound cycle of the illustration 650 is a heart sound waveform(e.g., a first heart sound waveform), the first S1 candidate 660 wouldbe the first candidate of the heart sound waveform (e.g., candidateheart sound (1,1)), the second S1 candidate 661 would be the secondcandidate of the heart sound waveform (e.g., candidate heart sound(1,2)), and the third S1 candidate 662 would be the third candidate ofthe heart sound waveform (e.g., candidate heart sound (1,3)).

FIG. 6C illustrates generally a diagram 670 including a heart soundwaveform 680 and exemplary heart sound waveforms. The exemplary heartsound waveforms include a time period 681 and a physiological cycle 682.The physiological cycle 682 includes multiple physiological cycles 690,a respiration cycle 685, a cardiac cycle 686, multiple cardiac cycles691, a heart sound cycle 687, and multiple heart sound cycles 692. Inother examples, the heart sound waveform can include at least a portionof one physiological cycle, including at least a portion of one cardiaccycle, etc. The heart sound waveform can also include multiplerespiration cycles.

FIG. 7 illustrates generally an example of a method 700 includingreceiving heart sound information and recognizing a first intra heartsound energy indication and a corresponding first intra heart sound timeindication within a particular heart sound of a particular heart soundwaveform. In an example, the first intra heart sound energy indicationand the corresponding first intra heart sound time indication can berecognized using the heart sound recognition circuit 210.

At 705, heart sound information can be received, such as by using theinput circuit 205.

At 710, a first intra heart sound energy indication and a correspondingfirst intra heart sound time indication can be recognized within aparticular heart sound of a particular heart sound waveform. In anexample, at 710, the first intra heart sound energy indication and thecorresponding first intra heart sound time indication can be recognizedusing the heart sound information from the particular heart soundwaveform and the heart sound information from at least one other heartsound waveform.

In an example, the recognizing the first intra heart sound energyindication and the corresponding first intra heart sound time indicationwithin the particular heart sound includes recognizing within at least aportion of one of S1, S2, S3, S4, or other portions or components of aheart sound signal. In an example, the recognizing the first intra heartsound energy indication and the corresponding first intra heart soundtime indication can correspond to the at least a portion of one of S1,S2, S3, S4, or other portions or components of the heart sound signal.

In the example of method 700, receiving the heart sound information caninclude receiving S2 information. The recognizing the first intra heartsound energy indication and the corresponding first intra heart soundtime indication within the particular heart sound of the particularheart sound waveform can include recognizing an intra S2 energyindication and a corresponding intra S2 time indication within an S2 ofthe particular waveform. Further, the using the heart sound informationfrom the particular heart sound waveform and the heart sound informationfrom the at least one other heart sound waveform can include using theS2 information from the particular heart sound waveform and the S2information from at least on other heart sound waveform.

In an example, the recognizing the first intra heart sound energyindication and the corresponding first intra heart sound time indicationcan include using a heart sound template. In an example, the using theheart sound template can include comparing the heart sound informationfrom the particular heart sound waveform to the heart sound template. Incertain examples, the heart sound information from the particular heartsound waveform can include at least one heart sound feature, such as amorphological feature. In an example, the using the heart sound templatecan include using a cross correlation between at least a portion of theheart sound information from the particular heart sound waveform and atleast a portion of the heart sound template. In an example, the usingthe cross correlation can include using a cross correlation between amorphology of the heart sound signal from the particular heart soundwaveform and at least a portion of the heart sound template, where themorphology includes multiple heart sound features, measurements,characteristics, etc., of the heart sound signal from the particularheart sound waveform.

In an example, the heart sound template can be updated using at least aportion of the heart sound information. In certain examples, the usingthe at least a portion of the heart sound information can include usingat least a portion of the heart sound information from the at least oneother heart sound waveform.

FIG. 8 illustrates generally an example of portions of a method 800including implantably sensing a heart sound signal and implantablydetecting at least one heart sound feature. In an example, the heartsound signal can be implantably sensed using the heart sound sensor 220.In an example the at least one heart sound feature can be detected usingthe heart sound feature detector 225.

At 805, a heart sound signal can be implantably sensed. The heart soundsignal can include any signal indicative of at least a portion of the atleast one heart sound of the subject (e.g. S1, S2, S3, S4, or anycomponents thereof, such as A2, P2, etc. In an example, the heart soundsignal can be sensed using the heart sound sensor 220.

At 810, at least one heart sound feature can be implantably detected.The at least one heart sound feature can be detected using the heartsound signal. Generally, the at least one heart sound feature caninclude at least one measurement, characteristic, morphology,computation, or interval of at least a portion of at least one heartsound.

FIG. 9 illustrates generally an example of portions of a method 900including detecting at least one candidate heart sound for theparticular heart sound of the particular heart sound waveform and the atleast one other heart sound waveform. In an example, the at least onecandidate heart sound can be detected using the detection circuit 230.

At 905, at least one first candidate heart sound for the particularheart sound of the at least one other heart sound waveform can bedetected. In an example, the at least one first candidate heart soundcan be detected using the heart sound information. The detecting the atleast one first candidate heart sound can include detecting an intraheart sound energy indication and a corresponding intra heart sound timeindication. Generally, the at least one other heart sound waveformexcludes the particular heart sound waveform. In an example, the atleast one other heart sound waveform can include the immediatelypreceding heart sound waveform to the particular heart sound waveform.In other examples, the at least one other heart sound waveform caninclude other preceding heart sound waveforms to the particular heartsound waveform, or the at least one other heart sound waveform caninclude heart sound waveforms occurring later in time than theparticular heart sound waveform.

At 910, at least one second candidate heart sound for the particularheart sound of the particular heart sound waveform can be detected. Inan example, the at least one second candidate heart sound can bedetected using the heart sound information. The detecting the at leastone second candidate heart sound can include detecting an intra heartsound energy indication and a corresponding intra heart sound timeindication.

In an example, the method 900 can further include recognizing the firstintra heart sound energy indication and the corresponding first intraheart sound time indication using the at least one detected firstcandidate heart sound and the at least one detected second candidateheart sound.

FIG. 10 illustrates generally an example of portions of a method 1000including calculating a cost for at least one candidate heart sound andrecognizing the first intra heart sound energy indication and thecorresponding first intra heart sound time indication using thecalculated cost. By calculating the cost of the at least one candidateheart sound, a desirable heart sound candidate for a particular heartsound waveform can be determined. In certain examples, the calculatingthe cost includes using a dynamic programming method, such as theViterbi method or other dynamic programming method. In certain examples,the cost can be calculated using the cost analysis circuit 235, and thefirst intra heart sound energy indication and the corresponding firstintra heart sound time indication can be recognized using the heartsound recognition circuit 210.

At 1005, a cost can be calculated for the at least one second candidateheart sound. The calculating the cost can include at least one ofcalculating a jump penalty and calculating a local score. Calculatingthe jump penalty can include calculating a temporal cost associated withthe at least one second candidate heart sound. In an example,calculating the jump penalty can include calculating the time differencebetween the second candidate heart sound and a first candidate heartsound. Typically, calculating the local score can include calculating alocal benefit associated with the at least one second candidate heartsound. In an example, calculating the local score can includecalculating the amplitude of the second candidate heart sound. In otherexamples, the calculating the jump penalty or the calculating the localscore can include weighting the calculating to improve or optimize thecost calculation.

In an example, calculating the cost can include calculating a totalscore. Calculating the total score can include reducing a previous totalscore by the jump penalty, and then adding the local score to themaximum result of the reduced previous total score. (See, e.g., Eq. 1).

At 1010, the first intra heart sound energy indication and thecorresponding first intra heart sound time indication can be recognizedusing the calculated cost. In an example, the recognizing the firstintra heart sound energy indication and the corresponding first intraheart sound time indication can include recognizing the candidate heartsound having the least cost, or the maximum total score.

In other examples, once the first intra heart sound energy indicationand the corresponding first intra heart sound time indication have beenrecognized, they can be stored, such as stored in a table, or stored inmemory.

FIG. 11 illustrates generally an example of portions of a method 1100including calculating a back pointer. In an example, the back pointercan be calculated using the heart sound recognition circuit 210. At1105, a back pointer can be calculated. Generally, the back pointer canbe indicative of the lowest cost path through multiple heart soundcandidates of multiple heart sound waveforms.

In an example, the calculating the back pointer can include selectingthe candidate heart sound having the maximum difference between theprevious total score of the candidate heart sound and the current jumppenalty. (See, e.g., Eq. 2).

FIG. 12 illustrates generally an example of portions of a method 1200including disregarding the recognized first intra heart sound energyindication and the corresponding recognized first intra heart sound timeindication and recapturing the disregarded recognized first intra heartsound energy indication and the corresponding disregarded recognizedfirst intra heart sound time indication. In certain examples, therecognized first intra heart sound energy indication and thecorresponding recognized first intra heart sound time indication can bedisregarded using the coasting circuit 240, and the disregardedrecognized first intra heart sound energy indication and thecorresponding disregarded recognized first intra heart sound timeindication can be recaptured using the recapture circuit 245.

In certain examples, if the heart sound information from a particularheart sound waveform is different than the heart sound information fromprevious heart sound waveforms, then the different heart soundinformation can be disregarded, e.g., by skipping over the recognizedfirst intra heart sound energy indication and the correspondingrecognized first intra heart sound time indication for that particularheart sound waveform. Similarly, if the heart sound informationcontinues to be different, a buffered version of the disregardedrecognized first intra heart sound energy indication and correspondingdisregarded recognized first intra heart sound time indication can berecaptured.

At 1205, the recognized first intra heart sound energy indication andthe corresponding recognized first intra heart sound time indication canbe disregarded. Generally, if the calculated cost of a recognized firstintra heart sound energy indication and corresponding first intra heartsound time indication is too high (e.g., above a threshold, or aboveprevious results), or if the total score of the recognized first intraheart sound energy indication and corresponding first intra heart soundtime indication is too low (e.g., below a threshold, or below previousresults), then the recognized first intra heart sound energy indicationand corresponding first intra heart sound time indication can bedisregarded.

In an example, the recognized first intra heart sound energy indicationand the corresponding recognized first intra heart sound time indicationcan be disregarded for a certain period (e.g., a certain number of heartsound waveforms, a certain period of time, etc.). In an example, if, atthe end of the certain period, the calculated cost remains too high, orif the total score remains too low, the disregarding can cease. This canbe indicative of a change (e.g., physical change, physiological change,system failure, environmental change, etc.). In an example, once it isdetermined that the heart sound information is relatively consistent(e.g., after disregarding for the certain period), the informationshould no longer be disregarded.

In an example, the recognized first intra heart sound energy indicationand the corresponding recognized first intra heart sound time indicationcan be disregarded, with the disregarding triggered using a comparison.The using the comparison can include using a comparison of therecognized first intra heart sound energy indication and thecorresponding recognized first intra heart sound time indication and atleast one other recognized intra heart sound energy indication and acorresponding at least one other recognized intra heart sound timeindication within the particular heart sound of at least one other heartsound waveform.

At 1210, the disregarded recognized first intra heart sound energyindication and the corresponding disregarded recognized first intraheart sound time indication can be recaptured. In an example, if thedisregarding occurs for the certain period, then it may be beneficial torecapture the disregarded recognized first intra heart sound energyindication and the corresponding recognized first intra heart sound timeindication (e.g., it may be beneficial if the heart sound informationhas changed, if the subject's status has changed, etc.). In an example,if the disregarding occurs for a period shorter than the certain period(e.g., the heart sound information is different for only a short time,such as one heart sound waveform), then it may not be beneficial torecapture the disregarded recognized first intra heart sound energyindication and the corresponding disregarded recognized first intraheart sound time indication (e.g., the disregarded information canconsist of noise or useless data).

In an example, the disregarded recognized first intra heart sound energyindication and the corresponding disregarded recognized first intraheart sound time indication can be recaptured, with the recapturingtriggered using a comparison. The comparison can include a comparison ofthe disregarded recognized first intra heart sound energy indication andthe corresponding disregarded recognized first intra heart sound timeindication and at least one other recognized intra heart sound energyindication and a corresponding at least one other recognized intra heartsound time indication within the particular heart sound of at least oneother heart sound waveform.

FIG. 13 illustrates generally an example of a system 1300 including animplantable medical device 215, an input circuit 205, and a heart soundrecognition circuit 210. The implantable medical device 215 can includea heart sound sensor 220 and a heart sound feature detector 225. Incertain examples, the implantable medical device 215 can include animplantable cardiac rhythm management (CRM) device, such as a pacer,defibrillator, cardiac resynchronization therapy (CRT) or other such CRMdevice. In this example, the implantable medical device 215 is implantedin a subject 201. Generally, the heart sound sensor 220 can beconfigured to sense a heart sound signal of the subject 201. The heartsound feature detector 225 is coupled to the heart sound sensor 220 andcan be configured to receive the heart sound signal from the heart soundsensor 220. In an example, the heart sound feature detector 225 can beconfigured to detect at least one feature of at least a portion of atleast one heart sound.

In an example, the input circuit 205 can be communicatively coupled tothe implantable medical device 215, and can be configured to receiveheart sound information from the heart sound sensor 220, or at least oneheart sound feature from the heart sound feature detector 225. In anexample, the heart sound recognition circuit 210 is coupled to the inputcircuit 205, and can be configured to receive heart sound informationfrom the input circuit 205. Generally, the heart sound recognitioncircuit 210 can be configured to recognize, within a particular heartsound of a particular heart sound waveform, a first intra heart soundenergy indication and a corresponding first intra heart sound timeindication using the heart sound information from the particular heartsound waveform and the heart sound information from at least one otherheart sound waveform.

The recognized first intra heart sound energy indication and thecorresponding recognized first heart sound time indication can be usedto detect heart failure (HF) decompensation. In an example, an improvedS3 amplitude and timing recognition can provide earlier HFdecompensation detection than other HF decompensation detection methods(e.g., thoracic impedance HF decompensation detection).

In the examples of FIG. 1-13, various examples, including receivingheart sound information, recognizing a first intra heart sound energyindication and a corresponding first intra heart sound time indication,implantable sensing a heart sound signal, implantable detecting at leastone heart sound feature, detecting at least one heart sound candidate,calculating a cost for the at least one heart sound candidate,calculating a back pointer, disregarding the recognized first intraheart sound energy indication and the corresponding recognized firstintra heart sound time indication, or recapturing the disregardedrecognized first intra heart sound energy indication and thecorresponding disregarded recognized first intra heart sound timeindication, are disclosed. It is to be understood that these examplesare not exclusive, and can be implemented either alone or incombination, or in various permutations or combinations.

It is to be understood that the above description is intended to beillustrative, and not restrictive. For example, the above-describedembodiments (and/or aspects thereof) may be used in combination witheach other. Many other embodiments will be apparent to those of skill inthe art upon reviewing the above description. The scope of the inventionshould, therefore, be determined with reference to the appended claims,along with the full scope of equivalents to which such claims areentitled. In the appended claims, the terms “including” and “in which”are used as the plain-English equivalents of the respective terms“comprising” and “wherein.” Also, in the following claims, the terms“including” and “comprising” are open-ended, that is, a system, device,article, or process that includes elements in addition to those listedafter such a term in a claim are still deemed to fall within the scopeof that claim. Moreover, in the following claims, the terms “first,”“second,” and “third,” etc. are used merely as labels, and are notintended to impose numerical requirements on their objects.

The Abstract is provided to comply with 37 C.F.R. § 1.72(b), whichrequires that it allow the reader to quickly ascertain the nature of thetechnical disclosure. It is submitted with the understanding that itwill not be used to interpret or limit the scope or meaning of theclaims. Also, in the above Detailed Description, various features may begrouped together to streamline the disclosure. This should not beinterpreted as intending that an unclaimed disclosed feature isessential to any claim. Rather, inventive subject matter may lie in lessthan all features of a particular disclosed embodiment. Thus, thefollowing claims are hereby incorporated into the Detailed Description,with each claim standing on its own as a separate embodiment.

1. A system, comprising: an input circuit, configured to receive heartsound information; a heart sound recognition circuit, coupled to theinput circuit, configured to recognize, within a particular heart soundof a particular heart sound waveform, a first intra heart sound energyindication and a corresponding first intra heart sound time indicationusing the heart sound information from the particular heart soundwaveform and the heart sound information from at least one other heartsound waveform; wherein the particular heart sound includes at least aportion of one of S1, S2, S3, and S4; and wherein the first intra heartsound energy indication and the corresponding first intra heart soundtime indication corresponds to the at least a portion of one of S1, S2,S3, and S4, respectively.
 2. The system of claim 1, wherein the inputcircuit is configured to receive S2 information; and wherein the heartsound recognition circuit is configured to recognize, within the S2 ofthe particular heart sound waveform, an intra S2 energy indication and acorresponding intra S2 time indication using the S2 information from theparticular heart sound waveform and the S2 information from at least oneother heart sound waveform.
 3. The system of claim 1, wherein the heartsound waveform includes at least a portion of at least one physiologicalcycle.
 4. The system of claim 3, wherein the physiological cycleincludes a cardiac cycle.
 5. The system of claim 3, wherein theparticular heart sound of a particular heart sound waveform includes anensemble averaged heart sound over multiple physiological cycles.
 6. Thesystem of claim 1, wherein the at least one other heart sound waveformincludes an immediately preceding heart sound waveform to the particularheart sound waveform.
 7. The system of claim 1, wherein the heart soundrecognition circuit is configured to recognize the first intra heartsound energy indication and the corresponding first intra heart soundtime indication using a heart sound template.
 8. The system of claim 7,wherein the heart sound template includes at least a portion of theheart sound information from the at least one other heart soundwaveform.
 9. The system of claim 8, wherein the heart sound recognitioncircuit is configured to recognize the first intra heart sound energyindication and the corresponding first intra heart sound time indicationusing a cross correlation between at least a portion of the heart soundinformation from the particular heart sound waveform and at least aportion of the heart sound template.
 10. The system of claim 1,including: an implantable medical device, the implantable medical deviceincluding: a heart sound sensor, configured to sense a heart soundsignal; and a heart sound feature detector, coupled to the heart soundsensor, the heart sound feature detector configured to detect at leastone heart sound feature using the heart sound signal; and wherein theheart sound information includes the at least one heart sound feature.11. The system of claim 1, wherein the heart sound recognition circuitincludes a detection circuit, the detection circuit configured to:detect at least one first candidate heart sound for the particular heartsound of the at least one other heart sound waveform using the heartsound information, wherein the at least one first candidate heart soundincludes an intra heart sound energy indication and a correspondingintra heart sound time indication; and detect at least one secondcandidate heart sound for the particular heart sound of the particularheart sound waveform using the heart sound information, wherein the atleast one second candidate heart sound includes an intra heart soundenergy indication and a corresponding intra heart sound time indication;and wherein the heart sound recognition circuit is configured torecognize the first intra heart sound energy indication and thecorresponding first intra heart sound time indication using: the atleast one detected first candidate heart sound; and the at least onedetected second candidate heart sound.
 12. The system of claim 11,wherein the at least one other heart sound waveform includes animmediately preceding heart sound waveform to the particular heart soundwaveform.
 13. The system of claim 11, wherein the heart soundrecognition circuit includes a cost analysis circuit, coupled to thedetection circuit, the cost analysis circuit configured to calculate acost for the at least one second candidate heart sound, the calculatedcost including: a jump penalty indicative of a temporal cost associatedwith the at least one second candidate heart sound; and a local scoreindicative of a local benefit associated with the at least one secondcandidate heart sound; and wherein the heart sound recognition circuitis configured to recognize the first intra heart sound energy indicationand the corresponding first intra heart sound time indication using thecalculated cost.
 14. The system of claim 13, wherein the heart soundrecognition circuit is configured to calculate a back pointer thatindicates a pointer from the at least one second candidate heart soundto an optimal at least one first candidate heart sound using the costanalysis.
 15. The system of claim 1, wherein the heart sound recognitioncircuit includes a coasting circuit, coupled to the heart soundrecognition circuit, configured to disregard the recognized first intraheart sound energy indication and the corresponding recognized firstintra heart sound time indication using a comparison of: the recognizedfirst intra heart sound energy indication and the correspondingrecognized first intra heart sound time indication; and at least oneother recognized intra heart sound energy indication and a correspondingat least one other recognized intra heart sound time indication withinthe particular heart sound of at least one other heart sound waveform.16. The system of claim 15, wherein the heart sound recognition circuitincludes a recapture circuit, coupled to the coasting circuit,configured recapture the disregarded recognized first intra heart soundenergy indication and the corresponding disregarded recognized firstintra heart sound time indication using a comparison of: the disregardedrecognized first intra heart sound energy indication and thecorresponding disregarded recognized first intra heart sound timeindication; and at least one other recognized intra heart sound energyindication and a corresponding at least one other recognized intra heartsound time indication within the particular heart sound of at least oneother heart sound waveform.
 17. A system, comprising: means forreceiving heart sound information; and means for recognizing a firstintra heart sound energy indication and a corresponding first intraheart sound time indication within a particular heart sound of aparticular heart sound waveform using the heart sound information fromthe particular heart sound waveform and the heart sound information fromat least one other heart sound waveform.
 18. The system of claim 17,including: means for disregarding the recognized first intra heart soundenergy indication and the corresponding recognized first intra heartsound time indication.
 19. The system of claim 18, including: means forrecapturing the disregarded recognized first intra heart sound energyindication and the corresponding disregarded recognized first intraheart sound time indication.
 20. A method, comprising: receiving heartsound information; recognizing a first intra heart sound energyindication and a corresponding first intra heart sound time indicationwithin a particular heart sound of a particular heart sound waveformusing the heart sound information from the particular heart soundwaveform and the heart sound information from at least one other heartsound waveform; wherein the recognizing the first intra heart soundenergy indication and the corresponding first intra heart sound timeindication within the particular heart sound includes recognizing withinat least a portion of one of S1, S2, S3, and S4; and wherein therecognizing the first intra heart sound energy indication and thecorresponding first intra heart sound time indication corresponds to theat least a portion of one of S1, S2, S3, and S4, respectively.
 21. Themethod of claim 20, wherein the receiving the heart sound informationincludes receiving S2 information; wherein the recognizing the firstintra heart sound energy indication and the corresponding first intraheart sound time indication within the particular heart sound of theparticular heart sound waveform includes recognizing an intra S2 energyindication and a corresponding intra S2 time indication within an S2 ofthe particular heart sound waveform; and wherein the using the heartsound information from the particular heart sound waveform and the heartsound information from the at least one other heart sound waveformincludes using the S2 information from the particular heart soundwaveform and the S2 information from at least one other heart soundwaveform.
 22. The method of claim 20, wherein the heart sound waveformincludes at least a portion of at least one physiological cycle.
 23. Themethod of claim 22, wherein the physiological cycle includes a cardiaccycle.
 24. The method of claim 22, wherein the particular heart sound ofthe particular heart sound waveform includes an ensemble averaged heartsound over multiple physiological cycles.
 25. The method of claim 20,wherein the using the heart sound information from the at least oneother heart sound waveform includes using the heart sound informationfrom an immediately preceding heart sound waveform to the particularheart sound waveform.
 26. The method of claim 20, wherein therecognizing the first intra heart sound energy indication and thecorresponding first intra heart sound time indication includes using aheart sound template and comparing the heart sound information from theparticular heart sound waveform to the heart sound template.
 27. Themethod of claim 26, wherein the using the heart sound template includesupdating the heart sound template using at least a portion of the heartsound information from the at least one other heart sound waveform. 28.The method of claim 26, wherein the recognizing the first intra heartsound energy indication and the corresponding first intra heart soundtime indication includes cross correlating between at least a portion ofthe heart sound information from the particular heart sound waveform andat least a portion of the heart sound template.
 29. The method of claim20, including: implantably sensing a heart sound signal; implantablydetecting at least one heart sound feature using the heart sound signal;and wherein the using the heart sound information includes using the atleast one heart sound feature.
 30. The method of claim 20, including:detecting at least one first candidate heart sound for the particularheart sound of the at least one other heart sound waveform using theheart sound information, wherein detecting the at least one firstcandidate heart sound includes detecting an intra heart sound energyindication and a corresponding intra heart sound time indication;detecting at least one second candidate heart sound for the particularheart sound of the particular heart sound waveform using the heart soundinformation, wherein detecting the at least one second candidate heartsound includes detecting an intra heart sound energy indication and acorresponding intra heart sound time indication; and wherein therecognizing the first intra heart sound energy indication and thecorresponding first intra heart sound time indication includes using:the at least one detected first candidate heart sound; and the at leastone detected second candidate heart sound.
 31. The method of claim 30,wherein the recognizing the at least one first candidate heart sound forthe particular heart sound of the at least one other heart soundwaveform includes recognizing the at least one first candidate heartsound for the particular heart sound of an immediately preceding heartsound waveform to the particular heart sound waveform.
 32. The method ofclaim 30, including calculating a cost for the at least one secondcandidate heart sound, including: calculating a jump penalty indicativeof a temporal cost associated with the at least one second candidateheart sound; and calculating a local score indicative of a local benefitassociated with the at least one second candidate heart sound; andwherein the recognizing the first intra heart sound energy indicationand the corresponding first intra heart sound time indication includesusing the calculated cost.
 33. The method of claim 32, includingcalculating a back pointer that indicates a pointer from the at leastone second candidate heart sound to an optimal at least one firstcandidate heart sound using the cost analysis.
 34. The method of claim20, including: disregarding the recognized first intra heart soundenergy indication and the corresponding recognized first intra heartsound time indication using a comparison of: the recognized first intraheart sound energy indication and the corresponding recognized firstintra heart sound time indication; and at least one other recognizedintra heart sound energy indication and a corresponding at least oneother recognized intra heart sound time indication within the particularheart sound of at least one other heart sound waveform.
 35. The methodof claim 34, including: recapturing the disregarded recognized firstintra heart sound energy indication and the corresponding disregardedrecognized first intra heart sound time indication using a comparisonof: the disregarded recognized first intra heart sound energy indicationand the corresponding disregarded recognized first intra heart soundtime indication; and at least one other recognized intra heart soundenergy indication and a corresponding at least one other recognizedintra heart sound time indication within the particular heart sound ofat least one other heart sound waveform.